The USDA Zone info is a great tool for gardeners to help us estimate your gardening schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

The USDA zone info for Billings should be reffered to in order to figure out when it's a good idea to plant primula.

Planting Calendar for Primula

Frost tolerance for primula:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Since primula are one of those plants that can tolerate quite a bit of cold weather you can plant them a lot earlier in the year than plants that are more sensitive to the cold.

The earliest that you can plant primula in Billings is March. However, you really should wait until April if you don't want to take any chances.

The last month that you can plant primula and expect a good harvest is probably August. If you wait any later than that and your primula may not have a chance to fully mature. If you are starting your primula indoors then you might be able to get away with starting them a little bit earlier.

Last Frost Date

In Billings the average date of last frost happens on May 15. You should expect an average low temperature of -25°F in the coldest months of winter.

Remember that USDA zone info for Billings is not always accurate and the actual date of last frost changes from year to year. Half of the time in Billings you get surprised by a frost after May 15 so just be sure to be ready to protect your primula in the event of a late frost.

USDA Zone Info for Billings

Here is the info for USDA Zone 4b.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-25°F
Highest Expected Low	-20°F

This means that on a really cold year, the coldest it will get is -25°F. On most years you should be prepared to experience lows near -20°F.

Plants to Grow in Billings

You may be interested in your other planting guides for Billings.